A hollow part with a flange formed at one end thereof is often used as an automobile part. A flange portion is used as a connecting substrate for connection to another member. With the main body formed to be hollow, the weight of the part as a whole is reduced. Conventionally, the hollow part of such a kind has been formed mainly of metal materials. However, attempts are now made to form lighter-weight hollow parts using fiber-reinforced resin.
Fiber-reinforced plastic (FRP) is a resin obtained by combining matrix resin such as thermosetting resin or thermoplastic resin with reinforced fibers. FRP has a light weight and excellent strength properties. Examples of thermosetting resin used include unsaturated polyester resin, epoxy resin, and polyimide resin. Examples of thermoplastic resin include polyethylene, polypropylene, and polyamide. Examples of reinforced fibers include carbon fibers, glass fibers, and aramid fibers.
There have been proposed several methods of forming hollow parts using fiber-reinforced resin. Among them is an internal-pressure molding method. The internal-pressure molding method includes the following steps: disposing a hollow molding material within a cavity of a shaping mold, applying internal pressure from within the hollow material to thereby make the hollow material closely attached to the shaping mold, and applying heat thereto to shape the hollow material. When a fiber-reinforced resin hollow part is molded using such an internal-pressure molding method, it is difficult to mold a flange portion integrally with the hollow part during the molding process. Thus, conventional fiber-reinforced resin hollow parts usually have no flange portions. Alternatively, even if they have flange portions, such flange portions are usually added later as appropriate to the fiber-reinforced resin hollow parts after the molding step.
Patent Document 1 describes an example of molding a fiber-reinforced resin hollow part with a non-uniform cross-section using the aforementioned internal-pressure molding method. According to Patent Document 1, a prepreg is wound around a mandrel with a circular cross-section and the mandrel is subsequently pulled out to form a hollow part made of the prepreg. Then, a pressure bag is inserted into a hollow portion of the hollow part made of the prepreg, and the hollow part with the pressure bag inserted therein is disposed in a mold having a shape corresponding to the non-uniform profile of the hollow part and in which a replenishing prepreg is arranged in the non-uniform profile portion. Then, the hollow part is molded by an internal-pressure molding method to obtain a hollow part made of FRP with a homogeneous non-uniform cross-section.
Patent Document 2 discloses a structural member for use in building construction and a method of manufacturing such a structural member, wherein a braid is formed by winding reinforced fibers around the circumference of a hollow cylindrical liner (a shaping material), which is made of an elastic material such as thermoplastic resin, by a braiding method, and the braid is disposed within a shaping mold, and then the reinforced fibers are impregnated with resin and cured. When the fibers are impregnated with resin, pressurized air is concurrently supplied to the liner (shaping material) to prevent deformation of the liner.    Patent Document 1: JP Patent Publication (Kokai) No. 2006-123475 A    Patent Document 2: JP Patent Publication (Kokai) No. 2003-328498 A